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An arbitrary SO user passed by, not a moderator, he had enough rep to protect the question without requiring assistance from a moderator or have his action subjected to review. Something anybody can do once they have 15,000 points.
His action has no connection whatsoever with your flag, or the reason a moderator declined it, he was completely unaware of ...

There are two answers from the same < 10 rep user, one with a -1 score, then deleted by the OP, then they made another answer shortly after, then self-deleted that. That triggered Community to protect the question to avoid that user trying the same again.
Update: The question has been unprotected as it's no longer required.

You can flag for a moderator using the "Other" flag reason, bring up your question here on Meta, or ask in a chat room related to the topic (so it will be likely to have 15k users).
Just make sure your question meets the criteria that will make protecting it worthwhile. Protecting a question only prevents new answers from users with less than 10 reputation, ...

From the Meta Stack Exchange protected FAQ post:
Why are some questions protected?
Some questions are protected because they are expected to attract either spam or users -- often new users -- who may mistake the site as a traditional forum, posting "noisy" answers such as "Thank you" or "This worked for me" or "I'm also having this problem".
and
...

You are requesting that we "Prevent protection of questions when it would have no effect".
Clearly, protecting questions does have an effect -- especially on high-traffic ones:
(More than 5 months later..)
I protected two of the questions you are using as examples.
Let's look at How do you create a remote Git branch?
This question hasn't received any ...

if I want to vote against the deletion, what action can/should i take ?
Fix the question. That is always, always the first action.
Can't fix the question?
Try to re-ask the question in a way that fits Stack Overflow guidelines and import over the content. That sometimes means separating a long answer into more small answer and question pair.
...

Users having over 15K rep can protect questions posted over a day ago (at some other sites, they can do this earlier than that), see What kind of questions should be protected?
This was the case in example referred in comments.
As for automatic protection by a Community user, it can be triggered in following cases:
When the third answer on a question ...

You requested that the question be protected due to copycat answers. I'm not the moderator who declined your flag, but the copycat answers you refer to were all posted by users with hundreds to even thousands of reputation points (and I did check the rep history of all the recent posters to see if they had that much at the time of posting). There were no ...

Although closing a question is, effectively, protecting it from being answered by anyone (this is why the protection notice is masked, because it's redundant), protection and closure are two separate concepts; one does not affect the other.
Think of protection and closure as two distinct layers of restriction, with protection being the inner, somewhat ...

While you can and should certainly also moderate old questions, consider just editing them to correct their deficits and preserve their usefulness.
I just did, and now the qustion should conform to the new site standards.
A more elaborate answer by Shog9, where he remodelled and reinstated a deleted recommendation-question.

If a question is off-topic with today's rules, close it as such, regardless of how many upvotes it has. This question asks for third-party tools or software, which is off-topic. Closing the question now will prevent that the question will collect opiniated and spammy answers.
When voting on such questions, which I would discourage, keep in mind that these ...

Community ignores answers that are deleted if the user asking them is also removed.
So if a question is attracting spam or nonsense answers such that the answers and the user asking them is getting deleted then you should protect the question to stop that. Here's an example question that needed manual protection. Of course you'll need 10K+ to see it in all ...

It was only protected to prevent more answers from getting added, it has 14 deleted ones right now. More significantly, the question has a hundred thousand views. Funny things happen when that many people view a question. Keep in mind that if 100,000 people looked at it then having 155 of them finding the question useful is not all that impressive ...

You have been served a review audit to see if you are paying attention and not just robo-clicking your way to a badge. The post has been 'massaged' a little to look like a first post, that's all.
Congratulations, you paid enough attention. Click No Action Needed (the post has stood the test of time), and pass the test.
You could consider the fact that the ...